linux-kernel - Re: [PATCH v2] sched/fair: check for idle core

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Date:   Fri, 23 Oct 2020 18:52:45 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...ia.fr>
To:     Chen Yu <yu.chen.surf@...il.com>
cc:     Julia Lawall <Julia.Lawall@...ia.fr>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] sched/fair: check for idle core



On Sat, 24 Oct 2020, Chen Yu wrote:

> On Fri, Oct 23, 2020 at 1:32 AM Julia Lawall <Julia.Lawall@...ia.fr> wrote:
> >
> [cut]
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index aa4c6227cd6d..9b23dad883ee 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -5804,6 +5804,9 @@ wake_affine_idle(int this_cpu, int prev_cpu, int sync)
> >         if (sync && cpu_rq(this_cpu)->nr_running == 1)
> >                 return this_cpu;
> >
> > +       if (available_idle_cpu(prev_cpu))
> How about also taking  sched_idle_cpu(prev_cpu) into consideration?
> if (available_idle_cpu(prev_cpu) || sched_idle_cpu(prev_cpu))

I have no opinion about this, because it wasn't relevant to the
application I was looking at.  The available_idle check on prev previously
in wake_affine_idle doesn't check sched_idle_cpu, so I didn't put it here.

julia